The objective of this research is to determine the effects of ultraviolet light on cell membranes. Studies of the primary steps in the photochemistry of biological membranes as well as studies of responses in relevant biological systems will be made. The results will be integrated to produce a fundamental understanding of the chemical, structural and functional modifications induced in membranes by ultraviolet light. Specifically, the research is intended to accomplish the following: 1) Describe the UVR-irradiation photochemistry of lipid bilayers containing aromatic amino acids. Hydrophobic oligopeptides incorporated into the bilayers of phospholipid liposomes will be irradiated and products and mechanisms of the photochemistry will be investigated. 2) Analyze the UVB-initiated chemical changes in biological membranes. Alterations in lipid and protein composition after UV irradiation will be studied in isolated erythrocyte membranes. 3) Determine how selected membrane structural and functional properties are altered by UVB irradiation. Bilayer fluidity will be assayed by fluorescence depolarization, membrane permeability to ions and small neutral species will be measured, and membrane enzyme activities will be assayed. 4) Test a hypothesis which connects UVB-induced lipid oxidation with the erythema response in skin. Studies of arachidonic acid release and prostaglandin synthesis in epidermal cells will be performed.